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“White tuna” is a marketing invention. 

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The "fake tuna" causes diarrhea. 

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Japan banned it in the 70s because of its effects on the human body.

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Terms like “sushi grade” are a rickroll. 

BRIEFING

Sloane here. Sushi carries a reputation for being clean, elevated, and tightly controlled, and most diners absorb that without a second thought. The setting feels curated, the language feels precise, and the assumption is that raw fish wouldn’t be served unless it met some higher bar, but that’s not the case. Time to dive in (literally).

Ordering tuna at a sushi restaurant feels like a safe choice. It’s familiar, widely accepted, and wrapped in the belief that “tuna is tuna.” In reality, that confidence is misplaced, especially when menus start using vague labels like “white tuna.”

Testing has shown that roughly three-quarters of fish sold as tuna at sushi-exclusive restaurants in the U.S. isn’t tuna at all. The most common substitute is escolar, a white fish that is much cheaper, visually appealing, and easy to sell under the loose term “oilfish.” It is marketed with premium-sounding language, but the words don’t actually tell you anything.

Despite being banned in Japan in 1977 (and briefly in the U.S. until the early 90s), escolar is not poisonous. It is, however, extremely fatty in a way most human bodies struggle to handle. It contains waxy oils that cannot be properly digested. In small amounts, some people notice nothing. In typical sushi portions, it can cause intense gastrointestinal distress hours later, long after the meal is over. This reaction is well known and directly tied to how the fish is metabolized.

In addition to there being no species called “white tuna,” there is also no official or regulated definition of “sushi-grade” fish. The term carries no enforcement and no standardized meaning. Instead, it serves as reassurance for customers and as leverage for sellers on pricing, not as a guarantee of safety or authenticity.

Appearance plays a huge role in maintaining this scrumptious, fatty white fish’s so-called premium look, and that look is achieved with carbon monoxide. The industry uses CO to redden fish and prevent browning as it ages, regardless of how it’s stored, making it easier to pass off as fresher or more desirable. For escolar, a solid white fish that doesn’t resemble tuna at all, this treatment is especially useful. Injected CO allows aging or misrepresented fish to hold onto a bright, high-end appearance that would normally raise eyebrows. It’s completely legal and has been used for decades.

This isn’t an argument against sushi, but once you know this, the menu reads very differently. Vague labeling, visual manipulation, and unregulated language quietly shift risk onto diners who assume transparency is built into the system.

Let's dive in and find out why escolar was removed from Japan’s food market decades ago. We can trace the decision back to its indigestible waxy fats and the digestive issues they cause in humans. The US restricted it in the 90s, but the fish later swam back in, under loose oversight and vague labeling. Now you'll see it sold as “white tuna,” despite not being tuna at all. It also details how escolar’s mild flavor and texture make it easy to substitute in sushi, especially when presentation and terminology do most of the marketing and convincing.

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Escolar was actually banned in Japan in 1977, but not because it's an exceptionally toxic or dangerous fish — it's because this fish causes keriorrhea in many, but not all, people. It is ... the unfriendly cousin of diarrhea. This fish, while delicious, is packed full of wax esters called gempylotoxin. The good news is that even though that word ends in "toxin," it's not actually toxic to humans.

Escolar cannot digest those fatty wax esters and stores them in its flesh and skin. This is relatable because when you eat this fish, you're eating tons of fats that you also cannot digest. The result seems like food poisoning but is actually more akin to eating a few bags of discontinued Lay's chips with olestra. It's not exactly pleasant, whatever it's called.

This professional fishmonger shows the butchering and consumption of a large portion of escolar... this is way more than what most people would eat in a single sitting. The reason he did this wasn't shock value but to demonstrate escolar’s digestive effects. Basically, this video shows how even someone experienced with fish treads carefully with this bugger.

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Jay Huang, a working sushi chef, explains how fish mislabeling actually happens behind the counter. He lays out why most deception isn’t about passing off red tuna as bluefin but about the much easier switch on the white side of the menu. Huang makes it clear there is no true “white tuna,” and that fish like escolar are marketed under that name to spark curiosity and justify those high prices.

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Other instances of misrepresentation would be with everyone’s favorite fish, tuna. Three main species of tuna are used in sushi restaurant: Yellowfin, Bigeye, and Bluefin. Bluefin can be further be identified as three different species: Northern Pacific, Southern Pacific, and Atlantic. This differentiation is important when I comes to sustainability (In another post).

The flavor and fat content of the three different species of tuna vary greatly. The Yellowfin is the most and mild, the Bigeye has medium to high fat content, and the Bluefin has the most flavor and fat content and is coveted for its O-toro, belly cut.

Restaurants will sometimes call Yellowfin Bigeye and charge the inflated price. However, it is difficult to pass off Yellowfin as Bluefin. The flavor and fat contrast is just to great. But, the misrepresentation of tuna is not usually with the red tuna but with the white. There is no true “white” tuna but sushi restaurants will market different fish as SUPER white tuna to intrigue guest into buying a fish they would otherwise pass up.

Escolar is one of these fish. It was banned in Japan in 1977 and also once banned in the United States in the early 90s, Escolar has made its way back onto Sushi menus in America as a popular fatty fish option. But, buyers beware, escolar has a waxy keto ester that is indigestible by humans and eating over 3 oz. of this fish, raw or cooked, can cause digestive problems that will have you running to the restroom.

There is no regulated definition of “sushi-grade” fish. The term has no official standard, certification process, or enforcement behind it.

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Sushi grade fish (or sashimi grade) is an unregulated term used to identify fish deemed safe for raw consumption. Most fish vendors will use the term "sushi grade" to indicate which of their supply is the freshest, highest quality, and treated with extra care to limit the risk of food-borne illnesses. This usually involves putting the fish through a freezing process before selling it.

There is no official standard for sushi grade fish, so you shouldn't place your full faith in a sushi grade label. Since it's unregulated, the term sushi grade may be used as an unfounded marketing ploy to upsell fish without consequences.

Although there are no actual guidelines in place to determine if a fish is sushi grade, the Food and Drug Administration (FDA) has regulations in place for the proper handling procedures of fish meant for raw consumption. The FDA has provided information on the different times and temperatures required for a variety of species of fish to be deemed safe.

While the treatment is legal, this helps explain how carbon monoxide treatment misleads consumers by disconnecting appearance from freshness, reinforcing that visuals do way more work than truth and transparency in seafood sales.

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Carbon monoxide-treated tuna is a process that exposes the fish to carbon monoxide gas. This treatment preserves the bright red color of the tuna, making it appear fresher for a longer period of time.

While this may seem like a harmless practice, it can have profound implications for consumers. CO is used to prevent oxidation, keeping the meat artificially red and fresh-looking even as it begins to deteriorate. This practice, while effective in maintaining its appearance, can be misleading for consumers who rely on color as an indicator of freshness.

DEBRIEFING

This is a system built on loose language, visual sneakiness, and the assumption that someone, somewhere, must be watching closely. They're not. In reality, much of the trust is implied rather than enforced.

When labels aren’t regulated, appearance becomes the new truth, and it's all a lie. Especially when color can be engineered, and names can be invented. This leaves diners relying on cues that are designed to reassure, not inform. Escolar is problematic because it’s often sold as something it isn’t, and our bodies aren't built to handle it.

Once you see how mislabeling, marketing language, and legal gray zones overlap, this stops being a sushi story and becomes one about how our rotten food system actually works.

NOW YOU KNOW

In sushi, trust is often built on presentation, not regulation.